"Solar Rain" video from NASA

Alternative History

I recently read A Palette of Particles, another fine book by the writer and physicist Jeremy Bernstein about the history of particle physics up to the Higgs boson. Bernstein mentions one chilling near miss in physics. In Rome in 1934 an Italian team led by Enrico Fermi actually observed nuclear fission. But they misinterpreted what they saw. Bernstein asks us to imagine how world history might have been different if fission was discovered in Fascist Italy in 1934 instead of four years later in Berlin 1938. Even though fission was discovered in Germany, by that time, the fascist powers were rapidly becoming very isolated from the rest of the scientific community. Lack of scientific knowledge might have been only part of the reason the Nazis weren't able to build a bomb, but it was probably a factor. After WWII several distinguished German scientists were held together by the Allies in England (Operation Epsilon) and their conversations were secretly recorded. Several of them, including Heisenberg, seemed surprised when they learned of the atomic bomb and may have mistakenly believed that an explosion would require tons of uranium, not kilograms.

The Variational Principles of Mechanics

I'm currently reading The Variational Principles of Mechanics by Cornelius Lanczos, the fourth edition published in 1970. From the preface to the first edition (1949):

The variational principles of mechanics are firmly rooted in the soil of that great century of Liberalism which starts with Descartes and ends with the French Revolution and which has witnessed the lives of Leibniz, Spinoza, Goethe, and Johann Sebastian Bach. It is the only period of cosmic thinking in the entire history of Europe since the time of the Greeks

The Action Principle may be the most profound principle in all of nature. The 18th century origins of the principle were colorful and controversial. Characters who were deeply involved included Émilie du Châtelet, an aristocratic lady; her lover, the writer Voltaire; and Fredrick the Great, King of Prussia! See The Berlin Academy and forgery.
Du Châtelet was a remarkable woman, her French translation of Isaac Newton's great work Principia Mathematica is still considered definitive. Café Gradot was the meeting place for intellectuals in Paris at the time, many of them her friends. When she tried to join her friends at their table, the management threw her out - women were not allowed in the cafés at the time. Undeterred, on later occasions she arrived attired as a man, and was able to participate in the discussions at the cafe without further incident.

The Big Higgs Questions

The Big Higgs Question by Nobel Prize winner Steven Weinberg in the New York Review of Books provides a history of the theory behind the Higgs Boson written by one of the key contributors.  The Higgs is important because previously known particles such as the W and Z, carriers of the weak nuclear force, are known to have a nonzero mass, but some mechanism needed to be added to the theory in order to give them a mass (particles can in fact be completely massless, for example the photon.)  There were other alternatives, but the Higgs mechanism was the leading candidate and the recent experiments at CERN pretty much confirmed the Higgs as the winner.  However, theorists are not finished being puzzled!  According to Weinberg, it would be much more "natural" if the Higgs mass were hundred thousand trillion times larger then what was just measured!  A slight discrepancy, for which there is currently no particularly good explanation.

"Now where did I leave that screwdriver?"
--- the other Big Higgs Question 

Walter Lewin at ESG

I had the pleasure of lunch today at MIT's Experimental Study Group (ESG). The special guest was Walter Lewin a retired MIT astrophysicist known for his popular online physics courses.
Professor Lewin is 76 but he still has a very sharp wit, however the MIT undergraduates were no slouches either.
He was asked, "What do you tell a student who doesn't like physics?"
"Well, I can tell you that they had a lousy teacher. That's the only possible reason. I can make anyone like physics. I can make a dog like physics."
Laughter from the students.
After being peppered with questions from the students for a half or hour or more, he was asked, "Do you have a favorite area of physics?"
"No."
"A least favorite area of physics?"
"Thermodynamics, I hate it"
"Did you have a lousy teacher?"
Everyone laughed including Professor Lewin.

Professor Lewin has a new book out For the Love of Physics.

Did Herman Weyl really prefer Beauty to Truth?

There's a famous quotation attributed to the mathematician and physicist Hermann Weyl:

My work always tried to unite the true with the beautiful; but when I had to choose one or the other, I usually chose the beautiful.

Contemporary physicists (in particular String Theorists) have been known to go on about how "beautiful" they find some theory (typically their own haha) especially when hard evidence to support that theory is nowhere in sight. There's usually a kind of tacit implication that the expositor is better in touch with the mysteries of the cosmos than the great unwashed who don't appreciate the "beauty" of their revolutionary new theory. After all the great Weyl valued Beauty over Truth didn't he? Peter Woit points out in a recent blog post Dyson on Fringe Physics, String Cosmology and Hermann Weyl that the context of that quote is quite significant and it's more than a little misleading to take it out of that context. It was published in a paper by Freeman Dyson in Nature on the occasion of Weyl's passing:

Characteristic of Weyl was an aesthetic sense which dominated his thinking on all subjects. He once said to me, half joking, ‘My work always tried to unite the true with the beautiful; but when I had to choose one or the other, I usually chose the beautiful’. This remark sums up his personality perfectly. It shows his profound faith in an ultimate harmony of Nature, in which the laws should inevitably express themselves in a mathematically beautiful form. It shows also his recognition of human frailty, and his humor, which always stopped him short of being pompous.

A particular example of this was Weyl's gauge theory of gravity, which turned out to be fatally flawed, but which he was reluctant to abandon because of its beauty. As it turns out, some of the principles that he used in this unworkable theory of gravity found use later on in other areas of physics. However, just because Weyl liked one of his theories that didn't work out at first, but some of the ideas later proved to be useful, doesn't mean the odds are particularly good at all for contemporary theorists with pet theories they claim to be beautiful. The libraries have aisles and aisles full of journals and dissertations which haven't turned out to be significant and it's extremely likely that the vast majority of them will never turn out to significant, not least because they often contradict each other!
The rest of Woit's blog post is worth reading too, as usual.

Ultra High Energy Cosmic Rays

Ultra High Energy Cosmic Rays hit the earth's atmosphere with energies millions of times higher than the most powerful man-made particle accelerator (the LHC). When these cosmic rays slam into the atmosphere, they create an air shower of up to billions of secondary particles which can be detected on the ground. They also generate a streak of ultraviolet light bright enough (barely) to be detected on the ground in ideal conditions. There are two amazing detector arrays: the Pierre Auger Observatory in Argentina; and the Telescope Array Project in Utah, which are currently collecting data using vast arrays of detectors. The recent preprint Ultra High Energy Cosmic Rays reviews the latest data gathered by these two observatories. One of the main unresolved questions is the source of these fantastically energetic particles - which particles are produced within our own Milky Way galaxy and which are extragalactic.

Top Quark Asymmetry

There are six quarks in the standard model of physics, the heaviest is the top quark. The Tevatron at Fermilab in Batavia, Illinois had earlier detected an unexpected asymmetry in top quark/antiquark production, but it wasn't overwhelmingly significant statistically speaking. New results in 2011 are more significant - see this preprint: Evidence for a Mass Dependent Forward-Backward Asymmetry in Top Quark Pair Production . There's a discussion at the Résonaances blog.

Renormalization

Quantum Field Theory (QFT)is the basic framework for both particle physics and condensed matter physics. However, disturbingly, QFT calculations are plagued by unwanted infinities. All too often, when we use the theory to calculate some observable property - for example, the mass of a particle - our calculation diverges, there is no finite solution. This can't be a good thing, especially when we find in our laboratories that the mass of that particle is indeed finite. Ordinarily, this would seem like a really good reason to throw up our hands and find ourselves a better theory. But theoretical physicists are made of sterner stuff. Whenever they stumble across one of these infinities they simply use the actual observed laboratory value instead. They then proceed with their calculations until they hit another observable infinity and do it again. For certain happy theories, clever people have proved that it's only necessary to resort to the process of kludging in laboratory values a finite number of times. The theory is then said to be renormalizable and the lucky physicist who creates such a theory may well get a Nobel Prize. Steven Weinberg got his Nobel Prize after the theory of electroweak interactions which he helped create was shown to be renormalizable. In the 2009 preprint Living with Infinities Weinberg discusses the problems with infinities in QFT.

Time Will End

The preprint Eternal inflation predicts that time will end argues that cosmological theories which include "eternal inflation" will lead to the end of time - their estimate is 5 billion years for our galaxy.  It may seem like you still have plenty of time, but it's never too soon to panic.

AntiNeutrino surprise at MINOS

One of the fundamental principles of particle physics is that particles and their anti-particles should have the same mass.  So it was a big surprise when Fermilab MINOS collaboration found that the muon neutrino and muon antineutrino appear to have different masses.  Neutrino experiments are extraordinarily difficult because neutrinos are so hard to detect.  This result is still very preliminary.  But if it does hold up, the impact on theoretical physics will be earthshaking.
See Neutrino surprise emerges from MINOS at PhysicsWorld .

Dimensionality of the Universe

One of the most mysterious facts about our universe is that, for most purposes, it can be modelled as four-dimensional: with one dimension for time and three dimensions for space. Why four, why not three, why not 42? There have long been proposals that add more dimensions, especially extra spatial dimensions, which are curled up so tightly that we don't normally perceive them.
The following preprint proposes something different. At very small scales (subatomic) there are effectively fewer than three spatial dimensions while at very large scales (cosmological) there are effectively more than three spatial dimensions!
Vanishing Dimensions and Planar Events at the LHC

We propose that the effective dimensionality of the space we live in depends on the length scale we are probing. As the length scale increases, new dimensions open up. At short scales the space is lower dimensional; at the intermediate scales the space is three-dimensional; and at large scales, the space is effectively higher dimensional. This setup allows for some fundamental problems in cosmology, gravity, and particle physics to be attacked from a new perspective. The proposed framework, among the other things, offers a new approach to the cosmological constant problem and results in striking collider phenomenology and may explain elongated jets observed in cosmic-ray data.

Event honoring Feynman.

TEDxCaltech, an exciting one-day event to honor Richard Feynman.

The Problem of Time

The Problem of Time in Quantum Gravity

The problem of time in quantum gravity occurs because `time' is taken to have a different meaning in each of general relativity and ordinary quantum theory. This incompatibility creates serious problems with trying to replace these two branches of physics with a single framework in regimes in which neither quantum theory nor general relativity can be neglected, such as in black holes or in the very early universe.

Testing the Universality of Free Fall

There's an interesting debate in Nature about atom interferometry tests of gravitational redshifts and what they imply about the university of free fall and the Einstein equivalence principle. See the preprint Atom gravimeters and gravitational redshift and the reply. See also the preprint Gravitational Redshift, Equivalence Principle, and Matter Waves. One of the authors in this controversy is Nobel prize winner and Department of Energy secretary Steven Chu.

A Light Sucker

Laser science: Suckers for light in Nature.

A Coherent perfect absorber is:

An optical device has been designed that performs a function exactly opposite to that of a laser. It perfectly absorbs incoming coherent radiation and turns it into thermal or electrical energy.

Backward lasing yields a perfect absorber

Just as a laser can emit coherent light from an amplifying medium, an absorbing medium can perfectly capture incoming radiation under the right conditions

CPA-based interferometers could thus have potential applications in the realization of transducers, modulators, or optical switches, for example, in on-chip integrated optical circuits based on Si waveguide/resonator technology.

Collider Physics

There is currently much excitement in physics due to the LHC, the huge new European particle accelerator. This preprint explains the theoretical analysis of such experiments: Introduction to Collider Physics.

Insertion of the vacuum-tank of the CMS detector in the LHC

How big is the Proton?

The proton shrinks in size: Tiny change in radius has huge implications - in Nature.

Topological Insulators

Topological insulators: Star material in Nature.
Topological insulators are a new kind of material which conduct electricity only on their surfaces. There are new, inexpensive compounds based on bismuth which have created a lot of excitement.
Solid-state physics: U-turns strictly prohibited also in Nature.

According to theory, electrons on the surface of a topological insulator are not allowed to make U-turns. This notion, and some of its main consequences, has now been tested experimentally.

Nuclear Reactions

Nuclear Reactions preprint.

Nuclear reactions generate energy in nuclear reactors, in stars, and are responsible for the existence of all elements heavier than hydrogen in the universe. Nuclear reactions denote reactions between nuclei, and between nuclei and other fundamental particles, such as electrons and photons. A short description of the conservation laws and the definition of basic physical quantities is presented, followed by a more detailed account of specific cases: (a) formation and decay of compound nuclei; (b)direct reactions; (c) photon and electron scattering; (d) heavy ion collisions; (e) formation of a quark-gluon plasma; (f) thermonuclear reactions; (g) and reactions with radioactive beams. Whenever necessary, basic equations are introduced to help understand general properties of these reactions. Published in Wiley Encyclopedia of Physics, ISBN-13: 978-3-527-40691-3 - Wiley-VCH, Berlin, 2009.